Bug#247436: marked as done (libc6-dev: odd dev_t/varargs behavior)
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and subject line Bug#247436: libc6-dev: odd dev_t/varargs behavior
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From: Andres Salomon <dilinger@voxel.net>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: libc6-dev: odd dev_t/varargs behavior
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Date: Wed, 05 May 2004 02:31:26 -0400
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Package: libc6-dev
Version: 2.3.2.ds1-12
Severity: normal
I'm seeing some very odd behavior with dev_t (defined in linux/kdev_t.h)
and varargs. I have the following source file:
#include <stdio.h>
#include <sys/types.h>
#include <linux/kdev_t.h>
int main(void)
{
dev_t x = 0x3af;
printf("%x %x\n", ((x)>>8), ((x)&0xff));
return 0;
}
One would think that this would print out "3 af"; however, it displays
"3 0". If I change that printf to:
printf("%x %x %x\n", ((x)>>8), ((x)&0xff));
I get "3 0 af". It would appear that dev_t, when passed as to a vararg
function, adds an additional argument as padding. So, when I pass "x>>8",
what printf() sees is "x>>8, 0". This doesn't happen normally; if I
change the definition of x to:
unsigned int x = 0x3af;
I get "3 af". Also, if I explicitly cast the args to unsigned int:
printf("%x %x\n", (unsigned int) ((x)>>8), (unsigned int) ((x)&0xff));
I get "3 af". So, it's some weird handling of dev_t's.
... I'm not quite sure what to make of it. I _think_ it's a glibc
problem..
-- System Information:
Debian Release: testing/unstable
APT prefers unstable
APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: i386 (i686)
Kernel: Linux 2.6.5-1-686
Locale: LANG=C, LC_CTYPE=C
Versions of packages libc6-dev depends on:
ii libc6 2.3.2.ds1-12 GNU C Library: Shared libraries an
ii linux-kernel-headers 2.5.999-test7-bk-15 Linux Kernel Headers for developme
-- no debconf information
---------------------------------------
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Subject: Re: Bug#247436: libc6-dev: odd dev_t/varargs behavior
From: Andres Salomon <dilinger@voxel.net>
To: Herbert Xu <herbert@gondor.apana.org.au>,
247436-done@bugs.debian.org
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References: <[🔎] E1BLJij-0005uH-00@gondolin.me.apana.org.au>
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On Wed, 2004-05-05 at 06:33, Herbert Xu wrote:
[...]
>=20
> Please review the C promotion rules.
>=20
> The 2nd and 3rd arguments are 64-bits long, and therefore they get pushed
> onto the stack as 64-bit values. Your use of the %x conversion is
> therefore incorrect.
>=20
> In fact, gcc -Wall should've told you about it.
Yes, I realized the problem after submitting the bug. Closing this...
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